1. Field of the Invention
The present invention relates to an apparatus for removing an off-set from a measured quantity containing an off-set.
2. Description of the Background Art
As an example of a conventional apparatus for removing an off-set from a measured quantity containing an off-set, there is a steering angle detection apparatus disclosed in Japanese Patent Application Laid Open No. 62-77210.
In a case a steering angle of a steering mechanism is detected by using a conventionally known steering angle sensor, the information concerning the steering angle measured from a central position in the steering mechanism can be obtained, but the central position in the steering mechanism may not necessarily coincide with a straight running position at which the car can be kept running straight, so that the signal from the steering angle sensor contains an off-set in addition to the desired steering angle information in a form of the steering angle with respect to the straight running position.
For this reason, the steering angle detection apparatus of the reference mentioned above comprises: a steering angle sensor for detecting a steering angle in the steering mechanism; an approximate central position sensor for detecting an angle range for an approximate central position in the steering mechanism; a quasi-central position calculation means for calculating a quasi-central position .theta..sub.CA as a mean displacement of a steering angle sensor signal .theta..sub.0 at a time of the approximate central position detection; and a steering angle calculation means for updating the central position .theta..sub.C by the quasi-central position .theta..sub.CA and for calculating a steering angle .theta. as a difference between the steering angle sensor signal .theta..sub.0 and the central position .theta..sub.C, such that it becomes possible to obtain the steering angle .theta.=.theta..sub.0 -.theta..sub.C with respect to the straight running position at which the car can be kept running straight.
However, in this conventional steering angle detection apparatus, while the car is running, if the signal from the quasi-central position detection sensor remains in an ON state for more than a prescribed distance, the central position .theta..sub.C is updated by the quasi-central position .theta..sub.CA obtained From the mean displacement of the steering angle sensor signal .theta..sub.0 from the steering angle sensor. Namely, in this conventional steering angle detection apparatus, the off-set is removed by using the quasi-central position sensor signal which,has the same physical dimension as the steering angle sensor signal .theta..sub.0. As a result, in a case of running on a high-way with continuous cornering at large radii, the quasi-central position .theta..sub.CA obtained by the quasi-central position calculation means can be considerably displaced from the actual central position, so that the steering angle .theta. obtained by the steering angle calculation means ends up having an off-set corresponding to this displacement of the quasi-central position .theta..sub.CA which is used to update the central position .theta..sub.C.
As a consequence, in a case of applying this conventional steering angle detection apparatus to a system for controlling dynamic characteristics of the car by using the steering angle .theta. as an input information, the controlling becomes such that the-desired dynamic characteristics of the car is not obtainable, due to the off-set contained in the steering angle information in addition to the actual value.
More specifically, in a case such a conventional steering angle detection apparatus is applied to a brake control system disclosed in Japanese Patent Application Laid Open No. 3-70663 by the present inventor, in which a steering angle and a yaw rate are entered as an input information, a target yaw rate appropriate for the steering angle is calculated, and the brake of each wheel is controlled as the signal is outputted to a brake actuator such that the input yaw rate and the target yaw rate coincide, the off-set for the steering angle .theta. to be given as an input information for obtaining the target yaw rate causes an unnecessary brake control in a non-cornering situation and an insufficient yaw rate characteristic in a curving situation.